Electrical igniter or fuse

ABSTRACT

An electrical igniter or fuse includes an electrically energized igniting means, an energizing circuit therefore and a condenser connected in the energizing circuit and acting as an electrical energy storage means. Normally open switch means are in series in the energizing circuit and are closed at a preselected time to discharge the condenser through the igniting means. A charging circuit for the condenser includes disengageable contacts for temporary connection to an extraneous source of potential to charge the condenser, and a spark gap switching means is interposed in the charging circuit between the condenser and the disengageable contacts. The extraneous source of potential has a potential higher than the firing potential of the glow tube constituting the spark gap switching means, and the condenser is charged to a potential lower than such firing potential. Thereby, when the contacts are disengaged from the potential source, shorting of the contacts will not effect discharge of the condenser.

United States Patent [\91 Held et a1.

[54] ELECTRICAL IGNITER OR FUSE [75] Inventors: Manfred Held, Poettmes; Johann Spies, Schlatzendorf/Pfahl, both of Germany [73] Assignee: Bolkow Gesellschaft mit beschrankter Haftung, Ottobrunn near Munich, Germany [22] Filed: June 28, 1968 [21] Appl. No.: 741,142

[ Foreign Application Priority Data July 6,1967 Germany ..P 15 78 447.1

[52] U.S. Cl. ..l02/70.2 R [51] Int. Cl ..F42b 11/06 [58] Field of Search ..102/70.2

[56] References Cited UNITED STATES PATENTS 1,711,693 5/1929 Ruhlemann ..lO2/70.2

1,807,708 6/1931 Ruhlemann ..102/70.2 2,545,474 3/1951 Kurland et al... ..l02/70.2

2,880,672 4/1959 Menke et a1 ..102/70.2

2,926,610 3/1960 Ruehlemann ..102/70.2 2,985,837 5/1961 Ruehlemann et al... ..102/70.2 3,001,477 9/1961 Ruehlemann et al ..lO2/70.2

Primary ExaminerVerlin R. Pendegrass A!t0rne v.lohn J. McGlew & Alfred E. Page [57] ABSTRACT An electrical igniter or fuse includes an electrically energized igniting means, an energizing circuit therefore and a condenser connected in the energizing circuit and acting as an electrical energy storage means. Normally open switch means are in series in the energizing circuit and are closed at a preselected time to discharge the condenser through the igniting means. A charging circuit for the condenser includes disengageable contacts for temporary connection to an extraneous source of potential to charge the condenser, and a spark gap switching means is interposed in the charging circuit between the condenser and the disengageable contacts. The extraneous source of potential has a potential higher than the firing potential of the glow tube constituting the spark gap switching means, and the condenser is charged to a potential lower than such firing potential. Thereby, when the contacts are disengaged from the potential source, shorting of the contacts will not effect discharge of the condenser.

8 Claims, 6 Drawing Figures PATENT- C 973 SHEET 1 UF 2 Figvl Fig.2

INVENTORS Manfred Held Johann Spiess maM/g/TTf NEYS PATEHTLS 1 55373 3.732.823

SHEET 2 U? 2 Manfred Held Johann piess By WMMM WM ATTORNEYS ELECTRICAL IGNITER OR FUSE BACKGROUND OF THE INVENTION There are known electrical igniters or fuses which do not have an active energy source individually associated therewith. These igniters or fuses generally include a condenser acting as an energy storage means and built into a projectile, for example, with the other components of the electrical ignition system. When the projectile leaves a launching tube, or just prior to the time the projectile leaves the launching tube, the condenser, through contacts connected therewith, is charged by an extraneous potential source which is fixedly connected with the launching tube. Such charging of the condenser is effected through contacts which extend through the outer jacket or shell of the projectile.

For example, German Patent No. 581,491 discloses an electrical igniter or fuse including a condenser acting as an energy storage means and a condensercharging circuit connected between the condenser electrodes and contacts arranged at the outer surface of a projectile jacket or enclosure. The contacts are arranged in such a manner that one of the electrodes of the condenser is connected directly to the projectile jacket and acts as a grounded contact, while the other electrode of the condenser is connected with a contact insulated from the jacket of the projectile. This latter contact is so constructed that, with the aid of mechanical covering means, it is exposed or connectable only during the time of electrical connection of the condenser with the entraneous potential source on the launching tube. The contact is thus protected With respect to one desired contact with the jacket of the launching tube after charging of the condenser.

Such a mechanical covering of the contact which is insulated relative to the jacket of the projectile requires considerable expenditure with respect to manufacture and assembly of the projectile. Additionally, such an arrangement does not operate in an absolutely safe manner, since the mechanical cover means may become ineffective or inoperative, for example by soiling or the like. If that happens, satisfactory contact engagement during the charging of the condenser by the extraneous potential source would be prevented, or the soiling may result in the establishment of a conductive connection with the jacket of the projectile or the launching tube, after charging of the condenser.

SUMMARY OF THE INVENTION This invention relates to electrical igniter or fuses for providing an igniting impulse at a preselected time and, more particularly, to an improved electrical igniter or fuse including a condenser serving as an electrical energy storage means and charged from an extraneous source of potential, the igniter or fuse being provided with means inhibiting accidential discharge of the condenser after charging thereof.

In accordance with the invention, an electrical igniter or fuse is provided in such a manner that, by means of very simple components, a safe connection of the condenser with an extraneous energy source is established during charging of the condenser, the connection having the smallest possible contact resistance. Furthermore, safe and secure electrical separation of the condenser from the remaining parts of the projectile, and thus from all other parts which possibly could come into contact with the jacket of the projectile, is effected with almost infinitely large contact or electrical resistance.

The electrical igniter or fuse of the invention releases an ignition impulse after a preselected delay period and, for this purpose, includes'afirst condenser serving as an energy storage means and which is charged to a preselected potential, for energizing an igniting means, by connection to an extraneous source of potential through disengageable contacts which connect the condenser only momentarily to the extraneous source. The condenser discharges through a delay circuit through the igniting means. In accordance with the invention, isolation of the condenser from other parts of the projectile or the like, or prevention of accidental discharge of the condenser, is provided by interposing, between the condenser and the disengageable contacts, at least one spark gap switching means through which charging of the condenser is effected from the extraneous potential source. By connecting at least one condenser electrode with a contact which is insulated relative to the jacket of the projectile through such a spark gap switching means, a nearly ideal electrical connection of the condenser is obtained during charging from the extraneous electrical potential source, with very small contact resistance. By contrast, an almost ideal electrical isolation of the condenser from this contact, insulated relative to the projectile jacket, is accomplished after disengagement of the charging contacts from the mating contacts connected to the extraneous source of potential and fixed relative to the launching device. The connection and disconnection of the disengageable contacts takes place without movable parts and thus it is fool-proof and safe in respect to soiling or other disturbing influences which are possible particularly in military use.

In a preferred embodiment of the invention, the spark gap switching means advantageously is a glow tube, such as a neon tube, which is brought into its operating range only at a very high firing potential. By using such a glow tube, which is also known as an overvoltage suppresser or surge arrester, as the spark gap switching means, it can be arranged that the condenser, acting as the energy storage means of the projectile, can be charged only with very high charging potentials applied thereto such as, for example, 800 volts. Consequently, all potentials which are below the firing potential of the glow tube and which, incidentally or inadvertently, should be impressed upon the contacts connected to the condenser, cannot cause inadvertent and thus undesirable charging of the condenser. By operating such a glow tube in its firing range, only a very small voltage drop appears across the glow tube proper, so that the contact resistance of the connection, during the charging procedure, is so small that it may be disregarded.

In accordance with a further embodiment of the invention, the electrical igniter is constructed in such a manner that the maximumpotential to which the first condenser can be charged is smaller than the firing potential of the glow tube. This maximum voltage potential, which is present across the condenser after the charging procedure, is necessarily lower than the charging voltage or potential of the extraneous energy source. Thus, the maximum voltage across the condenser is thus lower, by an amount corresponding to the voltage drop across the glow tube during the charging procedure, than the potential of the extraneous or external source of potential. The magnitude of the charging potential is so chosen that it is only slightly larger than the firing potential of the glow tube, so that, due to the voltage drop across the glow tube during the charging procedure, the potential across the condenser after the charging procedure is smaller than the firing potential of the glow tube. Consequently, ignition or discharge of the glow tube by the potential across the condenser after the latter is charged is not possible.

In accordance with another embodiment of the invention, the charging potential of the extraneous potential source is smaller than the firing potential of the glow tube. However, for brief periods this charging potential has periodically repeating voltage peaks which are larger than the firing potential of the glow tube. By choosing a charging potential of this type, it is assured that the maximum potential across the condenser after the charging procedure will always be smaller than the firing potential of the glow tube. By virtue of this, a renewed ignition or firing of the glow tube by the potential across the condenser after charging thereof is prevented in the event that there should occur any undesired extraneous shorting of the charging contacts which extend to the outer jacket of the projectile.

As a further feature of the invention, the first condenser can be charged from the extraneous potential source through a charging resistance and an additional condenser, in a manner such that the potential across the first condenser increases in a stepwise manner. Thereby it is assured that the first condenser, by choosing of a predetermined number of charging steps, is charged to a predetermined potential level which is proportional to the number of charging steps. Thus, a time delay, between charging of the condenser and energization of the electrically energized igniting means, and proportional to the magnitude of the charging potential, is adjustable.

In accordance with a first embodiment of the invention, the delay circuit of the igniter is a switch controlled by a clock mechanism. This clock mechanism may be started directly during launching of the projectile, or, in an alternative procedure, it may be started at a later time, for example by an additional switch which is actuated upon impact of the projectile.

In accordance with another embodiment of the invention, the delay circuit of the igniter consists of an additional condenser which is connected with the first condenser through a switch preferably actuated by impact of the electrical igniter, this additional condenser being in parallel with a discharge circuit consisting of an additional spark gap switching means and the electrically energized igniting means.

An object of the invention is to provide an improved electrical igniter or fuse of the type having a condenser, serving as an energy storage means, and charged from an extraneous source of potential.

Another object of the invention is to provide such an electrical igniter or fuse which can be connected temporarily with the external source of potential in a very simple manner and with a very small contact resistance.

A further object of the invention is to provide such an electrical igniter or fuse including means safely electrically isolating the charged condenser from the remaining parts of the projectile, containing the igniter, and thus from all parts which could possibly come into contact with the jacket of the projectile.

Yet another object of the invention is to provide such an electrical igniter or fuse in which such isolation is effected with almost infinitely large contact resistance.

A further object of the invention is to provide such an electrical igniter or fuse in which the condenser is connected with disengageable contacts, arranged to connect the condenser, during charging, temporarily to an extraneous source of potential, through at least one spark gap switching means.

Still another object of the invention is to provide such an electrical igniter or fuse in which the spark gap switching means comprises a glow tube having a very high firing potential.

A further object of the invention is to provide such an electrical igniter for a fuse in which the maximum potential to which the condenser can be charged is smaller than the firing potential of the glow tube.

Another object of the invention is to provide such an electrical igniter or fuse in which the charging potential of the extraneous source of potential is somewhat in excess of the firing potential of the glow tube.

A further object of the invention is to provide such an electrical igniter or fuse in which the charging potential of the extraneous source of potential is less than the firing potential of the glow tube, but in which the extraneous source of potential has, for brief periods, periodically repeating voltage peaks which are larger than the firing potential of the glow tube.

A further object of the invention is to provide such an electrical igniter or fuse in which the condenser is charged from the extraneous potential source through a charging resistance and an additional condenser so that the potential of the condenser which acts as an electrical energy storage means increases in a stepwise manner.

Another object of the invention is to provide such an electrical igniter or fuse including a delay circuit in the form of a switch controlled by a clock mechanism.

A further object of the invention is to provide such an electrical igniter or fuse including a delay circuit consisting of an additional condenser connected with the energy storage condenser through a switch actuated by impact of the igniter, this additional condenser being connected in parallel with a discharge circuit consisting of an additional spark gap switching means and the electrically energized igniting means.

For an understanding of the principles of the invention, reference is made to the following description of typical embodiments thereof as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic wiring diagram of an electrical igniter or fuse embodying the invention and including a clock mechanism acting as a time delay means;

FIG. 2 is a schematic wiring diagram illustrating an electrical igniter or fuse embodying the invention and including an ignition condenser acting as a time delay means;

FIG. 3 is a graphical illustration of the course of the potential at the storage condenser when the charging potential is constant;

FIG. 4 is a graphical illustration of the course of the potential at the storage condenser when the charging potential has impulse-forming voltage peaks;

FIG. 5 is a schematic wiring diagram of an electrical igniter embodying the invention and having stepwise charging of the storage condenser; and

FIG. 6 is a graphical illustration of the course of the potentials in the electrical circuit shown in FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, the electrical igniter or fuse includes a condenser charging circuit having disengageable contacts In and lb which extend to the outer jacket of a projectile, which latter has not been illustrated, for connection to an extraneous source of potential which may be, for example, mounted on a launching tube for the projectile. Contacts la and 1b are connected with a first condenser 2 serving as an energy storage means. One electrode of condenser 2 is connected directly with contact 1b, while the other electrode of condenser 2 is connected with contact 1a through spark gap switching means 3.

Condenser 2 is connected in an energizing circuit for an electrically energized igniting means 4, which is connected in parallel with condenser 2 through a switch 5. Switch 5 is closed, after an adjustable delay time, by means of a clock mechanism 6 which has not been shown in detail.

In the embodiment of theigniter shown in FIG. 2, condenser 2 acts, through switch 5 and a charging resistance 7 in series with switch 5, on an additional condenser 8 which acts as an igniting condenser. Condenser 8, in turn, is connected through a further spark gap switching means 9 with the electrically energized igniting means 4.

In the embodiment of the invention shown in FIG. 2, switch 5 preferably is closed upon impact of the projectile, so that thereafter the charge of condenser 2 is transferred into igniting condenser 8, with the time constant of charging of condenser 8 being determined by the magnitude of igniting condenser 8 and charging resistance 7. If igniter condenser 8 is charged to an extent such that the firing potential of spark gap switching means 9 is attained, igniting condenser 8 will discharge instantaneously through spark gap switching means 9 which is then conductive. Electrically energized igniting means 4 is thereby energized to fire, for example, an explosive charge which has not been shown. The delay time between impact of the projectile and ignition of the explosive charge can be chosen freely by dimensioning the components 7 and 8 which determine the charging time of igniting condenser 8.

In the embodiments of both FIGS. 1 and 2, charging of condenser 2, serving as the energy storage means, is effected by engaging contacts In and lb with an extraneous electric potential source I0 immediately before launching of the projectile, for example through sliding or slipping contacts operable between the projectile and its launching tube (not shown). The charging potential ofthe extraneous source of electric potential 10 must be at least slightly higher than the firing potential ofspark gap switching means 3, in order that the latter may be made conductive.

FIG. 3 graphically represents the voltage course of potential 20 which is present at condenser 2 in accordance with the charging time t, the other coordinate representing potential values U. The magnitude of the firing potential 21 of spark gap switching means or glow tube 3, and the magnitude of charging potential 22 of extraneous electric potential source 10, are also graphically illustrated in FIG. 3. The potential 22 of source 10 needs to be larger than firing potential 21 of spark gap switching means 3 only by such an amount that the maximum potential 20 across condenser 2, conditioned upon the voltage drop through spark gap switching means 3 when the latter is triggered conductive, remains sufficiently less than the firing potential 21 of spark gap switching means 3. Thereby, it is assured that, even if there should take place a subsequent extraneous or external shorting of contacts la and 1b, discharge of condenser 2 through spark gap switching means 3 will not be possible, since the firing potential of spark gap switching means 3 cannot be attained by the potential across condenser 2.

FIG. 4 graphically illustrates the course of the potential 20 across condenser 2 upon application of a charging potential 23 from source 10. This potential 23, contrary to the charging potential 22 of FIG. 3, is not constant but has periodically recurring brief potential peaks. The firing potential of spark gap switching means 3 is exceededonly with the first occurring potential peak of charging voltage or potential 23, thereby to initiate charging of condenser 2. The constant part of charging potential 23 of source 10, however, is still at a value such that it will not be below the glow or discharge potential of spark gap switching means 3. Thereby, after occurrence of a first voltage peak,'the charging of condenser 2 will continue independently of a renewed occurrence of the voltage peaks. Such a charging potential 23 has the advantage that the potential 20 across condenser 2 after charging will, in any event, be smaller than the firing potential of spark gap switching means 3.

In the embodiment of the igniter shown in FIG. 5, an additional condenser 11 is connected in parallel with source 10 and is charged through a charging resistance 12. The potential 26 across condenser 11 is thus impressed on contacts la and lb of the electrical igniter proper.

As shown in FIG. 6, and due to the charging potential 22 of source 10, condenser 11 is charged through charging resistance 12, and the potential 26 across condenser 11 is available to charge condenser 2 of the electrical igniter only when the potential 26 across condenser ll equals the firing potential of spark gap switching means 5. In this manner, condenser 2 is charged in a stepwise manner to its charged potential 20, the spark gap switching means 3 being conductive only for very short periods, to wit, at the moment when the difference between voltage 26 of condenser 11 and potential 20 across condenser 2 is equal to or larger than the firing potential 21 of spark gap switching means 3. Condenser 11 then discharges very rapidly into condenser 2, so that spark gap switching means 3 is again extinguished. The number of successive recharging procedures from condenser II to condenser 2 supplies a direct measure with respect to the magnitude of the voltage 20 impressed across condenser 2, so that the magnitude of voltage 20 can be easily adjusted by a counting procedure.

The delay time between closing of switch 5, upon impact of the projectile, and ignition of the explosive charge (not shown) is determined not only by the magnitude of resistance 7 and of igniting condenser 8, but also by the magnitude of voltage 20 across condenser 2. By adjusting the magnitude of voltage 20 across condenser 2, the delay time between impact of the projectile and ignition of the explosive can be preselected directly.

While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.

What is claimed is:

1. In an electrical igniter or fuse, for providing an igniting impulse after a preselected delay time, of the type including a first condenser serving as an energy storage means and which, for the purpose of accelerating the peaking of the igniting impulse, is chargeable from an extraneous source of electric'potential through disengageable contacts, connected for a brief interval only, and at least one spark gap switch, and which condenser, through a delay means, is later discharged through an electrically energized igniting means, the improvement comprising, in combination, said first condenser having a preselected maximum charging voltage; said spark gap switch comprising a glow tube operated in its arcing voltage range and having an ignition potential larger than said maximum charging voltage and smaller, during at least certain periods, than the voltage of said potential source.

2. An electrical igniter or fuse, as claimed in claim 1, in which said glow tube has a very high ignition potential.

3. An electrical igniter or fuse, as claimed in claim 1, in which said source voltage has a constant value which is less than the ignition potential of said glow tube, and

includes short periodically repeated potential peaks having potential magnitudes greater than the ignition potential of said glow tube.

4. An electrical igniter or fuse, as claimed in claim 1, including a charging resistance and an additional condenser connected across said extraneous source of electric potential in advance of said disengageable contacts, whereby the voltage of said first condenser is increased, during charging thereof, in a stepwise manner.

5. An electrical igniter or fuse, as claimed in claim 1, in which said delay means includes a normally open switch closed after a delay time.

6. An electrical igniter or fuse, as claimed in claim 5, in which said normally open switch is closed responsive to impact of said igniter; and a delay circuit connected between said normally open switch means and said electrically energized igniting means including an additional condenser 8 charged from said first condenser upon closure of said normally open switch means.

7. An electrical igniter or fuse, as claimed in claim 6, including an additional spark gap switching means connected in said energizing circuit in series with said additional condenser and said electrically energized igniting means, said additional spark gap switching means being triggered conductive responsive to charging of said additional condenser to a predetermined potential by said first condenser.

8. An electrical igniter or fuse, as claimed in claim 5, including a clock mechanism operable to close said normally open switch after a predetermined delay time. =9 

1. In an electrical igniter or fuse, for providing an igniting impulse after a preselected delay time, of the type including a first condenser serving as an energy storage means and which, for the purpose of accelerating the peaking of the igniting impulse, is chargeable from an extraneous source of electric potential through disengageable contacts, connected for a brief interval only, and at least one spark gap switch, and which condenser, through a delay means, is later discharged through an electrically energized igniting means, the improvement comprising, in combination, said first condenser having a preselected maximum charging voltage; said spark gap switch comprising a glow tube operated in its arcing voltage range and having an ignition potential larger than said maximum charging voltage and smaller, during at least certain periods, than the voltage of said potential source.
 2. An electrical igniter or fuse, as claimed in claim 1, in which said glow tube has a very high ignition potential.
 3. An electrical igniter or fuse, as claimed in claim 1, in which said source voltage has a constant value which is less than the ignition potential of said glow tube, and includes short periodically repeated potential peaks having potential magnitudes greater than the ignition potential of said glow tube.
 4. An electrical igniter or fuse, as claimed in claim 1, including a charging resistance and an additional condenser connected across said extraneous source of electric potential in advance of said disengageable contacts, whereby the voltage of said first condenser is increased, during charging thereof, in a stepwise manner.
 5. An electrical igniter or fuse, as claimed in claim 1, in which said delay means includes a normally open switch closed after a delay time.
 6. An electrical igniter or fuse, as claimed in claim 5, in which said normally open switch is closed responsive to impact of said igniter; and a delay circuit connected between said normally open switch means and said electrically energized igniting means including an additional condenser 8 charged from said first condenser upon closure of said normally open switch means.
 7. An electrical igniter or fuse, as claimed in claim 6, including an additional spark gap switching means connected in said energizing circuit in series with said additional condenser and said electrically energized igniting means, said additional spark gap switching means being triggered conductive responsive to charging of said additional condenser to a predetermined potential by said first condenser.
 8. An electrical igniter or fuse, as claimed in claim 5, including a clock mechanism operable to close said normally open switch after a predetermined delay time. 